After spending half the afternoon debugging what turned out to be two very simple problems (a PHP parse error and a MySQL “wrong field name” mistake), I’ve finally managed to implement incoming trackback support on my blog.
For those of you who don’t blog or who don’t get excited by new ways of doing things, trackbacks are a way of letting other people know that you’ve cited/commented on one of their blog entries on your blog. It’s like writing a comment directly on my blog, but instead you write something on your blog and then send my blog a message to tell it this. That message then appears as if it was a comment, except it links to your blog entry instead.
For the technically minded people out there, trackbacks are implemented via normal HTTP. Your blog sends a request via POST to my trackback script (the URL for each entry is given on its individual page, under the comments), which then takes the information you supply and puts it into a database table. This data can then be retrieved when anyone requests the entry to see who is citing my work.
The next step is to get trackbacks displayed nicely on the site, perhaps under comments—I’m not too sure where I want to put them yet. Any trackbacks you send will be recorded in the database though, even if they don’t show up on the entry page at the moment. I also need to get round to adding an admin interface for my blog so that when I post an entry it automatically trackbacks the relevant entries on other sites (if necessary) and tells Pingomatic that I’ve updated my blog, as well as generating a new RSS feed.
If you’re interested in implementing trackbacks on your site, the technical specification is available free of charge. Although it was written by Six Apart (who I know a lot of bloggers have issues with), it’s an open specification and you can implement in your blog without any constraints or license fees.